| PhD Seminar

Name of the Speaker: Mr. Amritayan Chatterjee (EE22D014)
Guide: Dr. Sudharsanan
Venue: ESB-244 (Seminar Hall)
Online meeting link: https://meet.google.com/qfu-cjyu-qkw
Date/Time: 31st January 2025 (Friday), 2:00 PM
Title: Energy Efficient IR to Visible Wavelength Conversion in Lithium Niobate-Silicon Nitride Heterogeneous Platform

Abstract :

Second harmonic generation (SHG) has emerged as a crucial nonlinear optical process in integrated photonics, where incident photons of frequency ω combine to generate photons of frequency 2ω through χ (2) nonlinear interactions. The growing demand for compact, efficient, and scalable nonlinear optical devices has driven significant research interest in developing heterogeneous photonic platforms that can effectively harness this phenomenon. Among various material combinations, integrating lithium niobate (LiNbO3) with silicon nitride (SiN) has proven particularly promising, offering a unique combination of strong nonlinear properties and excellent low-loss waveguiding capabilities. LiNbO3 (LN) has long been celebrated for its exceptional nonlinear optical properties, including a high second-order nonlinear coefficient (d33 ≈ 30 pm/V) and a wide transparency window enabling efficient up-conversion of 1.55 μm. However, traditional bulk LN devices suffer from large footprints and challenging integration with contemporary Si photonic platforms. Furthermore, LN etching processes introduce surface roughness-induced scattering losses. The heterogeneous integration of thin-film LNOI with SiN on the same platform through wafer bonding enables strong optical confinement, enhanced nonlinear interactions, and reduced power requirements for frequency conversion compared to bulk LN while maintaining compatibility with existing Si fabrication processes. This integration also offers cost reduction, increased throughput, and expanded functionality compared to standalone platforms while minimizing interface losses for implementing various SHG techniques, each offering distinct advantages and trade-offs. Four approaches have emerged as leading candidates for phase matching in the LN-SiN platform, all utilizing the d33 nonlinear coefficient of X-cut LN in TE polarization mode: Modal Phase Matching (MPM), Quasi-Phase Matching (QPM), Grating-Assisted Phase Matching (GAPM), and Directional Coupler-based Resonant Phase Matching (DCRPM). This research aims to develop compact, low-power, high-efficiency SHG at 1.55 μm in the LN-SiN platform utilizing the most efficient method among the four. Ultra-high Q ring resonators will be implemented to facilitate low power efficient frequency conversion, leveraging their small mode volumes and reduced pump power requirements for wavelength conversion. The demonstrated SHG methodology in the LN-SiN platform can be extended to sum frequency generation (SFG), which is particularly beneficial in single-photon-based applications.